1. Field of the Invention
The present invention relates to an obstacle avoidance function of mobile apparatuses such as robots and, more particularly, to a method for avoiding a traveling obstacle.
2. Description of the Related Art
Conventionally, there have been provided mobile apparatuses such as automatic carts and autonomous-travel automobiles, and devices capable of generating travel paths typified by manipulators of industrial robots. Some of these autonomous mobile apparatuses have a function of avoiding an obstacle present on a travel path, such as the following documents 1, 2 and 3.
Document 1: Japanese unexamined patent publication No. H10-20916
Document 2: Japanese unexamined patent publication No. 2003-241836
Document 3: Takashi TSUBOUCHI, Tomohide NANIWA, Suguru ARIMOTO, “planning and navigation by mobile robot in the presence of multiple moving obstacles and their velocities” Journal of the Robotics Society of Japan, Vol. 12, No. 7, 1994 (pp. 1029-1037).
Here are described related arts disclosed in Document 1, 2 and 3 with reference to FIGS. 10, 11A, 11B, 12A and 12B.
FIG. 10 is a schematic view showing an obstacle avoidance operation disclosed in Document 1. FIGS. 11A and 11B are schematic views showing an obstacle avoidance operation disclosed in Document 2, where FIG. 11A shows a probability potential field of an obstacle in a coordinate system and FIG. 11B shows a probability potential field with a slope added. Further, FIG. 12A is a schematic perspective view showing an obstacle avoidance operation disclosed in Document 3, and FIG. 12B is a schematic plan view showing an obstacle avoidance operation disclosed in Document 3.
Referring to FIG. 10, a mobile apparatus 510 disclosed in Document 1 defines, as an interference check block 520, a three-dimensional space of a specified environmental range within which the mobile apparatus is movable. The interference check block 520 is divided into sectors of an arbitrary size, and each of the sectors checks whether or not the sector interferes with an obstacle 530 on the travel course. Document 1 provides an obstacle avoidance method including the generation of a path for avoiding interference of the mobile apparatus 510 and the obstacle 530 with each other based on interference check results in the individual sectors of the interference check block 520 shown in FIG. 10.
Referring to FIGS. 11A and 11B, a mobile apparatus 610 disclosed in Document 2 is located on a space defined by three axes, probability density U, positions X and Y. The mobile apparatus 610 calculates probabilities by a two-dimensional normal distribution present at a next time point from past positional information of a travel obstacle 630 acquired by a sensor (not shown) mounted on the mobile apparatus to generate a probability potential field shown in FIG. 11A. Thereafter, the mobile apparatus adds a slope directed toward a target position in the generated probability potential field, and selects a path based on an inclination of the slope. More specifically, referring to FIG. 11B, out of travel paths ca and cb, the mobile apparatus 610 selects the travel path cb crossing across before the travel obstacle 630 if the slope of the travel path cb up to the target position is steeper than the slope of the travel path ca. Document 2 provides an obstacle avoidance method for searching for a path directed toward a target position based on an inclination of the probability potential field sloped as shown in FIG. 11B.
Referring to FIGS. 12A and 12B, a mobile apparatus 710 disclosed in Document 3 is located on a space having three axes, time T, positions X and Y. The mobile apparatus 710 estimates a velocity vector of a travel obstacle 730 from information acquired by a sensor (not shown) mounted on the mobile apparatus. Thereafter, the mobile apparatus 710 regards a locus of the travel obstacle 730 predicted from the estimated velocity vector as an oblique circular cylinder 740 on a space-and-time coordinate system to select, out of path candidates A1, A2 for avoiding the 740, a path that provides earlier arrival time to a target position.
More specifically, referring to FIG. 12B, out of the travel paths A1 and A2, if the arrival time by the travel path A2 is earlier than the arrival time by the travel path A1, then the mobile apparatus 710 selects the travel path A2 that intersects a forward side of the travel obstacle 730 as viewed in its travel direction. Document 3 provides a method for avoiding an obstacle on the basis of a path selected as shown in FIGS. 12A and 12B.